1. Field of the Invention
The present invention relates to a member in which an amorphous carbon film coating is formed on the surface of a base material that contacts a fluid and to a method of manufacturing same. More particularly, it relates to art enabling the reduction of erosion caused by cavitation that may occur within the fluid.
2. Description of the Related Art
In hydraulic equipment in a vehicle, because an operating fluid flows at high speed, the parts of the operating fluid having a low pressure vaporize in the region of valves and the like that are part of the hydraulic equipment, and vapor bubbles (cavitation bubbles) occur. The phenomenon of cavitation occurs, in which these bubbles collapse and disappear in a short period of time (several microseconds to several tens of microseconds). When such cavitation bubbles collapse, a shock wave as much as several GPa is generated. By the action of this shock wave on the surfaces of valves, damage that is known as erosion occurs in the form of depressions that appear to be parts where the surface is dug into. As a result, the hydraulic equipment might exhibit vibration and a decrease in performance.
In order to suppress erosion caused by this type of cavitation, the surfaces of the valves that come into contact with the operating fluid may be treated with Tufftride. Also, the provision of a DLC (diamond like carbon) film coating on either or both of the surface of a check ball found in a check valve and the surface of the annular ball sheet that receives the check ball has been described in Japanese Patent Application Publication No. JP-A-2003-207001.
In recent years, however, with a shift to hybrid vehicles, new systems that regenerate the energy of the vehicle when running have been added. As a result, linear valves and the like that are found in such vehicles experience an increased number of operations, and there is a trend toward more operating fluid passing through these valves. Also, cavitation erosion of the surfaces of the valves that contact the operating fluid occurs more easily. For this reason, it is not possible to sufficiently suppress erosion by the current situation being one in which, although Tufftride treating is done to the surfaces of ferrous materials, and simply providing a coating of amorphous carbon (DLC film coating). In particular, depending upon the film forming conditions, there is a large difference in the characteristics, such as the structure of the film, the thickness of the film, the adhesion, the surface hardness, SP2 (graphite structure)/SP3 (diamond structure) ratio, hydrogen concentration, and metal additive concentration. Therefore, it is not possible to say that an amorphous carbon film coating has superior cavitation erosion resistance characteristics. Additionally, a valve coated by an amorphous carbon film coating (DLC film coating) in such an environment cannot be said to have sufficient adhesion, and there is a risk of it peeling.